Modular system and process for continuous deposition of a thin film layer on a substrate

ABSTRACT

A process and associated system for vapor deposition of a thin film layer on a photovoltaic (PV) module substrate is includes establishing a vacuum chamber and introducing the substrates individually into the vacuum chamber. The substrates are pre-heated as they are conveyed through the vacuum chamber, and are then conveyed in serial arrangement through a vapor deposition apparatus in the vacuum chamber wherein a thin film of a sublimed source material is deposited onto an upper surface of the substrates. The substrates are conveyed through the vapor deposition apparatus at a controlled constant linear speed such that leading and trailing sections of the substrate in a conveyance direction are exposed to the same vapor deposition conditions within the vapor deposition apparatus. The vapor deposition apparatus may be supplied with source material in a manner so as not to interrupt the vapor deposition process or non-stop conveyance of the substrates through the vapor deposition apparatus.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to the field ofthin film deposition processes wherein a thin film layer, such as asemiconductor material layer, is deposited on a substrate. Moreparticularly, the disclosed subject matter is related to a system andprocess for depositing a thin film layer of a photo-reactive material ona glass substrate in the formation of photovoltaic (PV) modules.

BACKGROUND OF THE INVENTION

Thin film photovoltaic (PV) modules (also referred to as “solar panels”or “solar modules”) based on cadmium telluride (CdTe) paired withcadmium sulfide (CdS) as the photo-reactive components are gaining wideacceptance and interest in the industry. CdTe is a semiconductormaterial having characteristics particularly suited for conversion ofsolar energy (sunlight) to electricity. For example, CdTe has an energybandgap of 1.45 eV, which enables it to convert more energy from thesolar spectrum as compared to lower bandgap (1.1 eV) semiconductormaterials historically used in solar cell applications. Also, CdTeconverts energy more efficiently in lower or diffuse light conditions ascompared to the lower bandgap materials and, thus, has a longereffective conversion time over the course of a day or in low-light(e.g., cloudy) conditions as compared to other conventional materials.

Solar energy systems using CdTe PV modules are generally recognized asthe most cost efficient of the commercially available systems in termsof cost per watt of power generated. However, the advantages of CdTe notwithstanding, sustainable commercial exploitation and acceptance ofsolar power as a supplemental or primary source of industrial orresidential power depends on the ability to produce efficient PV moduleson a large scale and in a cost effective manlier.

Certain factors affect the efficiency of CdTe PV modules in terms ofcost and power generation capacity of the modules. For example, CdTe isrelatively expensive and, thus, efficient utilization (i.e., minimalwaste) of the material is a primary cost factor. In addition, the energyconversion efficiency of the module is a factor of certaincharacteristics of the deposited CdTe film layer. Non-uniformity ordefects in the film layer can significantly decrease the output of themodule, thereby adding to the cost per unit of power. Also, the abilityto process relatively large substrates on an economically sensiblecommercial scale is a crucial consideration.

CSS (Close Space Sublimation) is a known commercial vapor depositionprocess for production of CdTe modules. Reference is made, for example,to U.S. Pat. No. 6,444,043 and U.S. Pat. No. 6,423,565. Within thedeposition chamber in a CSS process, the substrate is brought to anopposed position at a relatively small distance (i.e., about 2-3 mm)opposite to a CdTe source. The CdTe material sublimes and deposits ontothe surface of the substrate. In the CSS system of U.S. Pat. No.6,444,043 cited above, the CdTe material is in granular form and is heldin a heated receptacle within the vapor deposition chamber. The sublimedmaterial moves through holes in a cover placed over the receptacle anddeposits onto the stationary glass surface, which is held at thesmallest possible distance (1-2 mm) above the cover frame. The cover isheated to a temperature greater than the receptacle.

While there are advantages to the CSS process, the system is inherentlya batch process wherein the glass substrate is indexed into a vapordeposition chamber, held in the chamber for a finite period of time inwhich the film layer is formed, and subsequently indexed out of thechamber. The system is more suited for batch processing of relativelysmall surface area substrates. The process must be periodicallyinterrupted in order to replenish the CdTe source, which is detrimentalto a large scale production process. In addition, the deposition processcannot be readily stopped and restarted in a controlled manner,resulting in significant non-utilization (i.e., waste) of the CdTematerial during the indexing of the substrates into and out of thechamber, and during any steps needed to position the substrate withinthe chamber.

Accordingly, there exists an ongoing need in the industry for animproved system and method for economically feasible large scaleproduction of efficient PV modules, particularly CdTe based modules.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In accordance with an embodiment of the invention, a process is providedfor vapor deposition of a thin film layer, such as a CdTe layer, on aphotovoltaic (PV) module substrate. A “thin” film layer is generallyrecognized in the art as less than 10 microns (μm), although theinvention is not limited to any particular film thickness. The processincludes establishing a vacuum chamber and introducing the substratesindividually into the vacuum chamber. The substrates are pre-heated asthey are conveyed through the vacuum chamber. The heated substrates arethen conveyed in a serial (i.e., end-to-end) configuration into andthrough a vapor deposition apparatus in the vacuum chamber wherein athin film of a sublimated source material is deposited onto a topsurface of the substrates. The substrates are conveyed at a controlled,constant linear conveyance rate through the vapor deposition apparatussuch that the leading and trailing sections of the substrates in thedirection of conveyance are exposed to the same vapor depositionconditions within the vapor deposition apparatus. In this manner, adesired substantially uniform thickness of the film layer is obtained onthe surface of the continuously moving substrate.

Desirably, the vapor deposition apparatus is supplied with sourcematerial, for example a granular CdTe material, in a manner that doesnot require interruption of the continuous vapor deposition process orconveyance of the substrates through the vapor deposition chamber.

Variations and modifications to the process discussed above are withinthe scope and spirit of the invention and may be further describedherein.

In accordance with another embodiment of the present invention, a systemis provided for vapor deposition of a thin film layer, such as a CdTefilm layer, on photovoltaic (PV) module substrates. The system includesa vacuum chamber, which may be defined by a plurality of interconnectedmodules in a particular embodiment. The vacuum chamber includes apre-heat section, a vapor deposition apparatus, and a cool-down section.A conveyor system is operably disposed within the vacuum chamber and isconfigured for conveying the substrates in a serial arrangement from thepre-heat section, through the vapor deposition apparatus, and throughthe cool-down section. In the unique modular embodiment mentioned above,the conveyor system may include an individually controlled conveyorassociated with each respective module, wherein the plurality ofconveyors are controlled to achieve a desired conveyance rate of thesubstrates through the various sections of the vacuum chamber. The vapordeposition apparatus is configured for continuous vapor depositionwherein a thin film of a sublimed source material is deposited onto atop surface of the substrates as the substrates are continuouslyconveyed through the vapor deposition apparatus. The substrates areconveyed at a controlled constant linear conveyance rate through thevapor deposition apparatus to achieve a desired uniform thickness of thethin film layer on the surface of the substrate.

A feed system may be operably configured with the vapor depositionapparatus to supply the apparatus with source material, such as agranular CdTe material, without interrupting the continuous vapordeposition process or non-stop conveyance of the substrates through theapparatus.

Variations and modifications to the embodiment of the system assemblydiscussed above are within the scope and spirit of the invention and maybe further described herein.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, is set forth in the specification, which makesreference to the appended drawings, in which:

FIG. 1 is a plan view of an embodiment of a system in accordance withaspects of the invention; and,

FIG. 2 is a perspective view of the embodiment of the system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventionencompass such modifications and variations as come within the scope ofthe appended claims and their equivalents.

FIGS. 1 and 2 illustrate an embodiment of a system 10 configured forvapor deposition of a thin film layer on a photovoltaic (PV) modulesubstrate 14 (referred to hereafter as a “substrate”). The thin film maybe, for example, a film layer of cadmium telluride (CdTe). Although theinvention is not limited to any particular film thickness, as mentioned,it is generally recognized in the art that a “thin” film layer on a PVmodule substrate is generally less than about 10 microns (μm). It shouldbe appreciated that the present system is not limited to vapordeposition of a particular type of film layer, and that CdTe is just onetype of film layer that may be deposited by the system 10.

Referring to FIG. 1, the system 10 includes a vacuum chamber 16, whichmay be defined by any configuration of components. In the particularillustrated embodiment, the vacuum chamber 16 is defined by a pluralityof interconnected modules, as discussed in greater detail below. Ingeneral, the vacuum chamber 16 may be considered as the section orportion of the system 10 wherein a vacuum is drawn and maintained forthe various aspects of the vapor deposition process.

The system 10 includes a preheat section 18 within the vacuum chamber16. The preheat section 18 may be one or a plurality of components thatpreheat the substrates 14 as they are conveyed through the vacuumchamber 16. In the illustrated embodiment, the preheat section 18 isdefined by a plurality of interconnected modules 20 through which thesubstrates 14 are conveyed.

The vacuum chamber 16 also includes a vapor deposition apparatus 24downstream of the preheat section 18 in the direction of conveyance ofthe substrates 14. This apparatus 24 may be configured as a vapordeposition module 22 and is the component configuration wherein a sourcematerial, such as granular CdTe material, is sublimated and depositedonto the substrate 14 as a thin film layer. It should be readilyappreciated that various vapor deposition systems and processes areknown in the art, such as the CSS systems discussed above, and that thevapor deposition apparatus 24 is not limited to any particular type ofvapor deposition system or process.

The vacuum chamber 16 also includes a cool-down section 26 downstream ofthe vapor deposition apparatus 24. In the illustrated embodiment, thecool-down section 26 is defined by a plurality of interconnectedcool-down modules 28 through which the substrates 14 are conveyed priorto being removed from the system 10, as described in greater detailbelow.

The system 10 also includes a conveyor system that is operably disposedwithin the vacuum chamber 16. In the illustrated embodiment, thisconveyor system 16 includes a plurality of individual conveyors 66, witheach of the modules in the system 10 including a respective one of theconveyors 66. It should be appreciated that the type or configuration ofthe conveyors 66 is not a limiting factor of the invention. In theillustrated embodiment, the conveyors 66 are roller conveyors driven bya motor drive 67 (FIG. 2) that is controlled so as to achieve a desiredconveyance rate of the substrates 14 through a respective module, andthe system 10 overall.

The system 10 also includes a feed system 48 (FIG. 2) that is configuredwith the vapor deposition apparatus 24 to supply the apparatus 24 withsource material, such as granular CdTe material. The feed system 48 maytake on various configurations within the scope and spirit of theinvention, and functions so as to supply the source material withoutinterrupting the continuous vapor deposition process within the vapordeposition apparatus 24 or conveyance of the substrates 14 through thevapor deposition apparatus 24.

Referring to FIGS. 1 and 2 in general, the individual substrates 14 areinitially placed onto a load conveyor 46, which may include, forexample, the same type of driven roller conveyor 66 that is utilized inthe other system modules. The substrates 14 are first conveyed throughan entry vacuum lock station 34 that is upstream of the vacuum chamber16. In the illustrated embodiment, the vacuum lock station 34 includes aload module 36 upstream of a buffer module 38 in the direction ofconveyance of the substrates 14. A “rough” (i.e., initial) vacuum pump56 is configured with the load module 36 to drawn an initial vacuumlevel, and a “fine” (i.e., high) vacuum pump 58 is configured with thebuffer module 38 to increase the vacuum in the buffer module 38 toessentially the vacuum level within the vacuum chamber 16. Valves 62(e.g., gate-type slit valves or rotary-type flapper valves) are operablydisposed between the load conveyor 46 and the load module 36, betweenthe load module 36 and the buffer module 38, and between the buffermodule 38 and the vacuum chamber 16. These valves 62 are sequentiallyactuated by a motor or other type of actuating mechanism 64 in order tointroduce the substrates 14 into the vacuum chamber 16 in a step-wisemanner without adversely affecting the vacuum within the chamber 16.

Under normal operating conditions, an operational vacuum is maintainedin the vacuum chamber 16 by way of any combination of vacuum pumps 58,56, and 60. In order to introduce a substrate 14 into the vacuum chamber16, the valve 62 between the load module 36 and buffer module 38 isinitially closed and the load module is vented. The valve 62 between thebuffer module 38 and first pre-heat module 20 is closed. The valve 62between the load module 36 and load conveyor 46 is opened and theindividual conveyors 66 in the respective modules are controlled so asto advance a substrate 14 into the load module 36. At this point, thefirst valve 62 is shut and the substrate 14 is isolated in the loadmodule 36. The rough vacuum pump 56 then draws an initial vacuum in theload module 36. During this time, the fine vacuum pump 58 draws a vacuumin the buffer module 38. When the vacuum between the load module 36 andbuffer module 38 are substantially equalized, the valve 62 between themodules is opened and the substrate 14 is moved into the buffer module38. The valve 62 between the modules is closed and the fine vacuum pump58 increases the vacuum in the buffer module 38 until it issubstantially equalized with the adjacent pre-heat module 20. The valve62 between the buffer module 38 and pre-heat module 20 is then openedand the substrate is moved into the pre-heat module 20. The processrepeats for each subsequent substrate 14 conveyed into the vacuumchamber 16.

In the illustrated embodiment, the preheat section 18 is defined by aplurality of interconnected modules 20 that define a heated conveyancepath for the substrates 14 through the vacuum chamber 16. Each of themodules 20 may include a plurality of independently controlled heaters21, with the heaters 21 defining a plurality of different heat zones. Aparticular heat zone may include more than one heater 21.

Each of the preheat modules 20 also includes an independently controlledconveyor 66. The heaters 21 and conveyors 66 are controlled for eachmodule 20 so as to achieve a conveyance rate of the substrates 14through the preheat section 18 that ensures a desired temperature of thesubstrates 14 prior to conveyance of the substrates 14 into a downstreamvapor deposition module 22.

In the illustrated embodiment, the vapor deposition apparatus 24includes a module 22 in which the substrates 14 are exposed to a vapordeposition environment wherein a thin film of sublimed source material,such as CdTe, is deposited onto the upper surface of the substrates 14.The individual substrates 14 are conveyed through the vapor depositionmodule 22 at a controlled constant linear speed. In other words, thesubstrates 14 are not stopped or held within the module 22, but movecontinuously through the module 22 at a controlled linear rate. Theconveyance rate of the substrates 14 may be in the range of, forexample, about 10 mm/sec to about 40 mm/sec. In a particular embodiment,this rate may be, for example, about 20 mm/sec. In this manner, theleading and trailing sections of the substrates 14 in the conveyancedirection are exposed to the same vapor deposition conditions within thevapor deposition module 22. All regions of the top surface of thesubstrates 14 are exposed to the same vapor conditions so as to achievea substantially uniform thickness of the thin film layer of sublimatedsource material on the upper surface of the substrates 14.

The vapor deposition module 22 includes a respective conveyor 65, whichmay be different from the conveyors 66 in the plurality of upstream anddownstream modules. Conveyor 65 may be particularly configured tosupport the vapor deposition process within the module 22. In theembodiment illustrated, an endless slat conveyor 65 is configured withinthe module 22 for this purpose. It should be readily appreciated,however, that any other type of suitable conveyor may also be used.

The vapor deposition apparatus 24 is configured with a feed system 48(FIG. 2) to continuously supply the apparatus 24 with source material ina manner so as not to interrupt the vapor deposition process or non-stopconveyance of the substrates 14 through the module 22. The feed system48 is not a limiting factor of the invention, and any suitable feedsystem 48 may be devised to supply the source material into theapparatus 24. For example, the feed system 48 may include sequentiallyoperated vacuum locks wherein an external source of the material isintroduced as metered doses in a step-wise manner through the vacuumlocks and into a receptacle within the vapor deposition apparatus 24.The supply of source material is considered “continuous” in that thevapor deposition process need not be stopped or halted in order tore-supply the apparatus 24 with source material. So long as the externalsupply is maintained, the feed system 48 will continuously supplybatches or metered doses of the material into the vapor depositionapparatus 24.

In the illustrated embodiment, a post-heat section 30 is defined withinthe vacuum chamber 16 immediately downstream of the vapor depositionmodule 22. This post-heat section 30 may be defined by at least onepost-heat module 32 having a heater unit 21 configured therewith. As theleading section of a substrate 14 is conveyed out of the vapordeposition module 22, it moves into the post-heat module 32. Thepost-heat module 32 maintains the temperature of the substrate 14 atessentially the same temperature as the vapor deposition module 24. Inthis way, leading section of the substrate 14 is not allowed to coolwhile the trailing section is still within the vapor deposition module22. If the leading section of the substrate 14 were allowed to cool asit exited the module 22, a non-uniform temperature profile would begenerated longitudinally along the substrate 14. This condition couldresult in breaking, cracking, or warping of the substrate from thermalstress.

A cool-down section 26 is downstream of the post-heat section 30 withinthe vacuum chamber 16. The cool-down section 26 may include one or morecool-down modules 28 having independently controlled conveyors 66. Thecool-down modules 28 define a longitudinally extending section withinthe vacuum chamber 16 in which the substrates having the thin film ofsublimed source material deposited thereon are allowed to cool at acontrolled cool-down rate prior to the substrates 14 being removed fromthe system 10. Each of the modules 28 may include a forced coolingsystem wherein a cooling medium, such as chilled water, refrigerant, orother medium is pumped through cooling coils 29 configured with themodules 28, as particularly illustrated in FIG. 2.

An exit vacuum lock station 40 is configured downstream of the cool-downsection 26. This exit station 40 operates essentially in reverse of theentry vacuum lock station 34 described above. For example, the exitvacuum lock station 40 may include an exit buffer module 42 and adownstream exit lock module 44. Sequentially operated valves 62 aredisposed between the buffer module 42 and the last one of the modules 28in the cool-down section 26, between the exit buffer module 42 and theexit lock module 44, and between the exit lock module 44 and an exitconveyor 50. A fine vacuum pump 58 is configured with the exit buffermodule 42, and a rough vacuum pump 56 is configured with the exit lockmodule 44. The pumps 58, 60, and valves 62 are sequentially operated(essentially in reverse of the entry lock station 34) to move thesubstrates 14 out of the vacuum chamber 16 in a step-wise fashionwithout loss of vacuum condition within the vacuum chamber 16.

As mentioned, in the embodiment illustrated, the system 10 is defined bya plurality of interconnected modules, with each of the modules servinga particular function. For example, modules 36 and 38 function tointroduce individual substrates 14 into the vacuum chamber 16. Theconveyors 66 configured with these respective modules are appropriatelycontrolled for this purpose, as well as the valves 62 and associatedactuators 64. The conveyors 66 and heater units 21 associated with theplurality of modules 20 in the pre-heat section 18 are controlled topre-heat the substrates 14 to a desired temperature, as well as toensure that the substrates 14 are introduced into the vapor depositionmodule 22 at the desired controlled, constant linear conveyance rate.For control purposes, each of the individual modules may have anassociated independent controller 52 configured therewith to control theindividual functions of the respective module. The plurality ofcontrollers 52 may, in turn, be in communication with a central systemcontroller 54, as illustrated in FIG. 1. The central system controller54 can monitor and control (via the independent controllers 52) thefunctions of any one of the modules so as to achieve an overall desiredconveyance rate and processing of the substrates 14 through the system10.

Referring to FIG. 1, for independent control of the individualrespective conveyor 66, each of the modules may include any manner ofactive or passive sensors 68 that detect the presence of the substrates14 as they are conveyed through the module. The sensors 68 are incommunication with the module controller 52, which is in turn incommunication with the central controller 54. In this manner, theindividual respective conveyor 66 may be controlled to ensure that aproper spacing between the substrates 14 is maintained and that thesubstrates 14 are conveyed at the desired constant conveyance ratethrough the vacuum chamber 16.

The present invention also encompasses various process embodiments forvapor deposition of a thin film layer on a photovoltaic (PV) modulesubstrate. The processes may be practiced with the various systemembodiments described above or by any other configuration of suitablesystem components. It should thus be appreciated that the processembodiments according to the invention are not limited to the systemconfiguration described herein.

In a particular embodiment, the process includes establishing a vaporchamber and introducing PV substrates individually into the chamber. Thesubstrates are preheated to a desired temperature as they are conveyedthrough the vacuum chamber in a serial arrangement. The preheatedsubstrates are then conveyed through a vapor deposition apparatus withinthe vacuum chamber wherein a thin film of a sublimated source material,such as CdTe, is deposited onto the upper surface of the substrates. Thesubstrates are conveyed through the vapor deposition apparatus at acontrolled constant linear speed such that the leading and trailingsections of the substrates in a conveyance direction are exposed to thesame vapor deposition conditions within the vapor deposition apparatusso as to achieve a uniform thickness of the thin film layer on the uppersurface of the substrates.

In a unique embodiment, the vapor deposition apparatus is supplied withsource material in a manner so as not to interrupt the vapor depositionprocess or conveyance of the substrates through the vapor depositionapparatus.

The process may further include cooling the substrates downstream of thevapor deposition apparatus within the vacuum chamber prior to subsequentremoval of each of the cooled substrates from the vacuum chamber.

It may be desired to post-heat the substrates as they exit the vapordeposition apparatus prior to cooling the substrates such that theleading section of the substrates in the direction of conveyance is notcooled until the entire substrate has exited the vapor depositionapparatus. In this manner, the substrate is kept at a relativelyconstant temperature along its longitudinal length while the trailingsection of the substrate is undergoing the deposition process within thevapor deposition apparatus.

As mentioned, the substrates are conveyed through the vapor depositionapparatus at a constant linear speed. In a unique embodiment, thesubstrates may be conveyed through the other sections of the vacuumchamber at a variable speed. For example, the substrates may be conveyedat a slower or faster speed, or step-wise, as they are pre-heated beforethe vapor deposition apparatus, or as they are cooled after the vapordeposition apparatus.

The process may also include individually introducing the substratesinto and out of the vacuum chamber through an entry and exit vacuum lockprocess wherein the vacuum conditions within the vacuum chamber are notinterrupted or changed to any significant degree.

In order to sustain a continuous vapor deposition process, the processalso may include supplying the source material to the vapor depositionapparatus from an externally refillable feed system. The feed processmay include continuously introducing metered doses of the sourcematerial from the feed system into the vapor deposition apparatuswithout interrupting the vapor deposition process. For example, themetered doses of source material may be introduced through sequentialvacuum locks and deposited into a receptacle within the vapor depositionapparatus. In this manner, the vapor deposition process need not beinterrupted to refill the source material within the vapor depositionapparatus.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A process for vapor deposition of a thin film layer on a photovoltaicmodule substrate, comprising: establishing a vacuum chamber maintainedat an operation vacuum; introducing substrates individually into thevacuum chamber such that the vacuum chamber is maintained at theoperational vacuum; pre-heating the substrates as the substrates areconveyed through the vacuum chamber; and conveying the pre-heatedsubstrates in serial arrangement through a vapor deposition apparatus inthe vacuum chamber wherein a thin film layer of a sublimed sourcematerial is deposited onto an upper surface of the substrates in thevapor deposition apparatus; wherein the substrates are conveyed throughthe vapor deposition apparatus at a controlled constant linear speedsuch that leading and trailing sections of the substrate in a conveyancedirection are exposed to the same vapor deposition conditions within thevapor deposition apparatus to achieve a substantially uniform thicknessof the thin film layer on an upper surface of the substrate.
 2. Theprocess as in claim 1, further comprising cooling the substratesdownstream of the vapor deposition apparatus within the vacuum chamber,and subsequently individually removing each of the cooled substratesfrom the vacuum chamber.
 3. The process as in claim 2, furthercomprising post-heating the substrates as the substrates exit the vapordeposition apparatus and prior to cooling the substrates so that thesubstrates are not cooled until the entire substrate has exited thevapor deposition apparatus.
 4. The process as in claim 1, wherein thesubstrates are individually introduced into the vacuum chamber throughan entry vacuum lock process, and individually removed from the vacuumchamber through an exit vacuum lock process such that vacuum within thevacuum chamber is maintained during entry and exit of the substrates. 5.The process as in claim 1, wherein the vacuum chamber is defined by aplurality of interconnected modular units, with each of the modularunits having an independent conveyor, the process further comprisingcontrolling the individual conveyors to achieve an overall continuousflow of the substrates through the vacuum chamber at a desired heatingrate, vapor deposition rate, and cool down rate.
 6. The process as inclaim 1, wherein the vapor deposition apparatus is supplied with sourcematerial from an externally refillable feed system in a manner so as notto interrupt the vapor deposition process or non-stop conveyance of thesubstrates through the vapor deposition apparatus.
 7. The process as inclaim 1, wherein the source material is CdTe, and wherein the thin filmCdTe layer is deposited over a CdS thin film layer previously applied tothe substrates.
 8. The process as in claim 1, wherein the substratescomprise glass.
 9. A process for vapor deposition of a thin film layeron a photovoltaic module substrate, comprising: establishing a vacuumchamber maintained at an operation vacuum; introducing glass substratesindividually into the vacuum chamber such that the vacuum chamber ismaintained at the operational vacuum; pre-heating the glass substratesas the glass substrates are conveyed through the vacuum chamber; andconveying the pre-heated glass substrates in serial arrangement througha vapor deposition apparatus in the vacuum chamber wherein a thin filmlayer of a sublimed source material is deposited onto an upper surfaceof the glass substrates in the vapor deposition apparatus; wherein theglass substrates are conveyed through the vapor deposition apparatus ata controlled constant linear speed such that leading and trailingsections of the glass substrate in a conveyance direction are exposed tothe same vapor deposition conditions within the vapor depositionapparatus to achieve a substantially uniform thickness of the thin filmlayer on an upper surface of the glass substrate.
 10. The process as inclaim 9, further comprising cooling the glass substrates downstream ofthe vapor deposition apparatus within the vacuum chamber, andsubsequently individually removing each of the cooled glass substratesfrom the vacuum chamber.
 11. The process as in claim 10, furthercomprising post-heating the glass substrates as the glass substratesexit the vapor deposition apparatus and prior to cooling the glasssubstrates so that the glass substrates are not cooled until the entireglass substrate has exited the vapor deposition apparatus.
 12. Theprocess as in claim 9, wherein the glass substrates are individuallyintroduced into the vacuum chamber through an entry vacuum lock process,and individually removed from the vacuum chamber through an exit vacuumlock process such that vacuum within the vacuum chamber is maintainedduring entry and exit of the glass substrates.
 13. The process as inclaim 9, wherein the vacuum chamber is defined by a plurality ofinterconnected modular units, with each of the modular units having anindependent conveyor, the process further comprising: controlling theindividual conveyors to achieve an overall continuous flow of the glasssubstrates through the vacuum chamber at a desired heating rate, vapordeposition rate, and cool down rate.
 14. The process as in claim 9,wherein the vapor deposition apparatus is supplied with source materialfrom an externally refillable feed system in a manner so as not tointerrupt the vapor deposition process or non-stop conveyance of theglass substrates through the vapor deposition apparatus.
 15. The processas in claim 9, wherein the source material is CdTe, and wherein the thinfilm layer is deposited over a CdS thin film layer previously applied tothe glass substrates.
 16. A process for vapor deposition of a thin filmlayer on a photovoltaic module substrate, comprising: establishing avacuum chamber maintained at an operational vacuum; introducing glasssubstrates individually into the vacuum chamber such that the vacuumchamber is maintained at the operational vacuum; pre-heating the glasssubstrates as the glass substrates are conveyed through the vacuumchamber; conveying the pre-heated glass substrates in serial arrangementthrough a vapor deposition apparatus in the vacuum chamber; anddepositing a thin film CdTe layer onto an upper surface of the glasssubstrates in the vapor deposition apparatus; wherein the glasssubstrates are conveyed through the vapor deposition apparatus at acontrolled constant linear speed such that leading and trailing sectionsof the glass substrate in a conveyance direction are exposed to the samevapor deposition conditions within the vapor deposition apparatus toachieve a substantially uniform thickness of the thin film CdTe layer onan upper surface of the glass substrate.